Background technology
In the fluid bearing of the oil film pressure supporting rotating shaft that utilizes the lubricating oil in the gap of axle periphery and sleeve inner peripheral surface, either party at least at axle periphery or sleeve inner peripheral surface establishes dynamic pressure grooves, fluid dynamic pressure bearing between the slip of the oil-bound film that utilization is formed by its velocity pressure effect and floating supporting rotating shaft, or make porous insert immersion lubrication oil or the lubricating grease that constitutes by sintering metal etc., make it to have self-lubricating function, the stephanoporate oil-retaining bearing of supporting rotating shaft, and the velocity pressure type stephanoporate oil-retaining bearing of establishing dynamic pressure grooves at the bearing surface of stephanoporate oil-retaining bearing, be applicable to as the multi-point scanning electric motor of laser beam printer (LBP) or the spindle drive motor of disk drive (HDD) usefulness, as requiring the machine of high running accuracy, perhaps DVD-ROM at a high speed down, the spindle drive motor that the magneto-optical disc apparatus of the optical disc apparatus of DVD-RAM etc. or MO etc. is used is such, owing to the mounting disk and at the machine that applies high-speed driving under the condition of uneven loading.
In order to adapt to the low torque requirement of the small-sized spindle drive motor usefulness bearing of equipment for information about, fluid dynamic pressure bearing, stephanoporate oil-retaining bearing, velocity pressure type stephanoporate oil-retaining bearing etc. are selected the lower lubricating oil of viscosity for use.In the past, as low viscous lubricating oil, the hydro carbons, the spy that have proposed PAO (poly-alpha olefins) etc. open the described diester of flat 4-357318 communique, or the spy opens the described dialkyl carbonate of flat 8-259977 communique or polyol ester, the spy opens the described monoesters of 2000-63860 communique etc.
In recent years, along with popularizing of acoustic image, the high performance of office automation (AVOA) equipment, portable utilization etc., therefore small-sized spindle drive motor high speed, miniaturization that these rotating part of strong request uses, usually require rotary supporting part to divide the bearing low torqueization of using.Though influence the factor of bearing torque play of bearing, the diameter of axle etc. are arranged, oil body also becomes a big principal element.
The lower evaporation more easily of the general viscosity of lubricating oil.When lubricating oil reduced owing to evaporation waits, the oil film pressure that can not obtain suiting influenced the life-span because of running accuracy reduces, so the evaporation characteristic of lubricating oil is the key property of domination bearing weather resistance.Therefore, lubricating of sliding surface bearing such as fluid dynamic pressure bearing, stephanoporate oil-retaining bearing, velocity pressure type stephanoporate oil-retaining bearing must be selected low viscosity and evaporation characteristic lubricating oil preferably.And most situation is used the lubricating oil of ester class.
Ester oil has many kinds, and the characteristic of its viscosity, evaporation characteristic, solvability etc. is different respectively, in addition, and along with the tendency that reduces viscosity evaporation characteristic variation is identical with other lubricating oil.Therefore,, select low viscous ester oil for existing, damaged evaporation characteristic, the weather resistance of bearing is reduced in order to reduce the torque of bearing.For example, the low viscosity oil of monoesters etc. and mixing oil as the heavy oil of main body expect that steam output is few even the viscosity on apparent is high, reduce but low molecular composition optionally evaporates the back oil mass, perhaps low molecular composition optionally enters lubricated face, produces the problem that makes bearing rigidity reduction and so on.In addition, when using diester, by the lubricating oil of suitably selecting molecular weight can obtain to have low viscosity characteristics, if but 40 ℃ viscosity is 10mm
2The diester that/s is following, steam output increases with lower molecular weightization, produces evaporation basically simultaneously owing to the uniform cause of molecular weight simultaneously, so certain condition is reduced rapidly as the boundary weather resistance.
The working of an invention scheme
At first, explain the present invention with reference to accompanying drawing.
Fig. 4 and Fig. 5 are the sectional views of sintered metal bearing device and velocity pressure type sintered metal bearing device, and symbol is respectively 1-gasket, 2-stephanoporate oil-retaining bearing, 3-transverse bearing, 4-axle, 5-bearing housing, 6-sealing-gap, the existing edge axle of 7-band, 8-thrust bearing part, 9-cover cylindrical portions may, 10-cover thrust support section among the figure.
Therefore, consider the bearing assembly of structure shown in the C-1 of Fig. 5.This structure is that use being full of under the state of lubricating oil the cover internal space.
The enlarged view of steady state hermetic unit is shown in the C-3 of Fig. 6.Lubricated pasta is in the interior circumferential portion of gasket, and under the imagination condition of environment for use temperature, posture etc., the general design of lubricated pasta is in the such of the interior circumferential portion of gasket.Otherwise, in the time of on lubricated pasta rises to gasket upside end face, certainly lubricating oil is to the bearing assembly external leaks, when if lubricated pasta drops under the gasket downside end face, inclusion of air reduces running accuracy in the lubricating oil of bearing surface, simultaneously because the thermal expansion of air, the lubricating oil of inside is squeezed toward the bearing assembly outside, become the reason that causes oil leak.Lubricating oil is because the phenomenon as latter and so on takes place in evaporation.Therefore, as concrete design, the use minimum temperature that must design at bearing assembly (is a lubricating oil volume minimum, the state that the face position is minimum) under, make lubricated pasta position from the state of C-3 because evaporation changes to time of state of the C-4 of Fig. 6, the ratio device desired durable time of integral body is long.
Suppose, bearing assembly is under the environment of minimum use temperature, because the evaporation of lubricating oil is when the state of the C-3 of Fig. 6 becomes the state of C-4, the 3 weight % that account for the lubricating oil gross weight with the volume decrement reach the 10000 hours durable time that bearing assembly is required, as shown in Figure 7, under 10000 hours situation of placement,, then can not satisfy weather resistance if selected rate of evaporation is lower than the lubricating oil of 3 weight %.Like this, the weather resistance correlate of the evaporation characteristic of lubricating oil and the bearing assembly electric motor of this bearing assembly (or be assembled with) is selected the good lubricating oil of evaporation characteristic, and this is related to the long lifetime of bearing assembly.
In addition, though influence the factor of bearing torque play of bearing, the diameter of axle etc. are arranged, oil body also becomes a big principal element.By using the lower lubricating oil of viscosity, can reduce and stir resistance (viscous resistance), its torque as a result also reduces.
The lubricating oil that warm-up viscosity is different is the Fig. 8 that the results are shown in of the bearing assembly mensuration torque of structure shown in the C-1 that uses Fig. 5.As shown in Figure 8, the proportional relation of the kinematic viscosity of lubricating oil and torque as can be seen, the reduction of lubricating oil viscosity is directly connected to the reduction of bearing torque.
As previously discussed, provide the problem of long bearing assembly of low torque and life-span, can be resolved by selecting low viscosity and evaporation characteristic excellent lubrication oil.
Below, lubricant oil composition of the present invention is described.
As the base oil of lubricant oil composition main body is that carbonatoms is the ester of 10 di-carboxylic acid.When being the ester of the di-carboxylic acid more than 11 with carbonatoms, the torque during rotation is increased, and can not obtain the performance that needs.On the other hand, carbonatoms is 9 when following, and steam output increases rapidly, can not realize the long lifetime of spindle drive motor.Therefore, must be that the ester formed of 10 di-carboxylic acid is as principal constituent with carbonatoms.As carbonatoms is the preferably sebacic acid of linear saturated fatty acids of 10 di-carboxylic acid.
Be the pure composition that the ester of 10 di-carboxylic acid uses as above-mentioned carbonatoms, preferably carbonatoms is the monobasic representative examples of saturated aliphatic alcohol of 6-10, is more preferably octanol.Preferred particularly 2-ethylhexanol.Above-mentioned ester is relative straight chain shape, owing to do not have the big side chain of polyol ester and so on, so have high viscosity index (HVI), high flash point and good low-temperature fluidity.
Viscosity when preferably mixing 40 ℃ in base oil is less than 11mm
2/ s and the flash-point low-viscosity oil (minor component) more than 150 ℃.If the viscosity 11mm when mixing 40 ℃
2The above lubricating oil of/s then can not be realized low torqueization, also can encourage evaporation even mix flash-point for the mixing less than 150 ℃ low-viscosity oil optimum quantity.In other words, the viscosity ratio base oil of preferred low-viscosity oil is low, the low-viscosity oil that molecular-weight average is low.Therefore, low-viscosity oil as the minor component use, can use the DOZ (dioctyl azelate) that satisfies above-mentioned condition or DOA (adipic acid dioctyl ester), DOPCP, monoesters, PAO (poly-alpha olefins) etc., but consider from low-temperature fluidity, intermiscibility, oilness aspect, most preferably use to have and the DOZ that by carbonatoms is the ester similar structures that makes of 10 di-carboxylic acid and octanol.
In addition, as the ester of base oil and composition as the low-viscosity oil of minor component, with respect to the lubricant oil composition total amount, low-viscosity oil must be the scope of 3-20 weight %.Containing of low-viscosity oil is proportional when surpassing 20 weight %, the influence of minor component is quite obvious, and steam output increases, and can not prolong the life-span of spindle drive motor, and containing of low-viscosity oil is proportional when being lower than 3 weight %, can not obtain to reduce the unusual effect of torque.Promptly, the present invention mixes low-viscosity oil as minor component by optimum quantity ground in as the ester of base oil, low viscosity and the low steam output do not made clear are had concurrently in the past, mix as low viscous minor component by optimum quantity, minor component with low molecular composition optionally imports between lubricated face, realizing low torqueization, is that the ester that 10 di-carboxylic acid is formed causes the spindle drive motor long lifetime as the carbonatoms that suppresses the evaporation composition.
Lubricant oil composition of the present invention also can mix known additives such as antioxidant, extreme-pressure additive, the agent of anti-friction damage, rust-preventive agent, metal passivator, oiliness activator as required.
Lubricant oil composition of the present invention can be preferably velocity pressure type sintered metal bearing with, fluid dynamic pressure bearing with, stephanoporate oil-retaining bearing with, velocity pressure type stephanoporate oil-retaining bearing with aspect use.
Embodiment
Below, enumerate embodiment and comparative example, make the present invention clearer and more definite.
Use the diester shown in the table 1 as base oil, use the low-viscosity oil shown in the table 2 as minor component.Cooperating base oil, low-viscosity oil, other additive shape in the ratio shown in table 3~table 6 is lubricant oil composition.To be shown in table 3~table 6 to the result or the evaluation result of this lubricant oil composition mensuration rate of evaporation and kinematic viscosity (40 ℃).In addition, the Fig. 1 that the results are shown in of the rate of evaporation of ester of comparative example 1~4 and kinematic viscosity (40 ℃) will be measured.Table 4~table 6 show lubricant oil composition to use carbonatoms as the base oil of main body be the ester (sebacic acid two-2-ethylhexyl ester) of 10 di-carboxylic acid, prepare the lubricating oil of several changes, estimate the result of rate of evaporation and kinematic viscosity (40 ℃) as the blending ratio of the low-viscosity oil of minor component.Also have, in the comparative example shown in table 3~table 6 and embodiment, add same amount the known oxidation inhibitor of conduct alkyl diphenylamine and as the benzotriazole of metal passivator and as the trioctyl phosphate of anti-friction damage agent.In addition, in table 4~table 6, use level is a weight part, the residual content when the lubricated constituent total amount of residue representation is 100 weight parts.
Table 1
Expression | ????C6 | ????C9 | ????C10 | ????C12 |
Compound name | Adipic acid two-2-diethyl acetamidomalonate | Nonane diacid two-2-ethylhexyl ester | Sebacic acid two-2-ethylhexyl ester | Dodecanedioic acid two-2-ethylhexyl ester |
40 ℃ of kinematic viscosity mm
2/s
| ????7.8 | ????10.4 | ????12.0 | ????13.5 |
Flash-point ℃ | ????204 | ????208 | ????224 | ????228 |
Table 2
Expression | ??PAO3 | ??POE1 | ????MP |
The goods name | ??2.5 | ??HATCOL?2957 | ????60 |
Content | Poly-alpha olefins | DOPCP | Naphthenic base oil |
Producer's name | Xie Tian swells the Phillips chemistry | ??HATCO | |
40 ℃ of kinematic viscosity mm
2/s
| ??8.3 | ??7.5 | ????7.8 |
Flash-point ℃ | ??186 | ??182 | ????140 |
Table 3
| Composition | Comparative example |
????1 | ????2 | ????3 | ????4 | ????5 | ????6 | ????7 |
Cooperate | ??C12 | Residue | ????- | ????- | ????- | ????- | ????- | ????- |
??C10 | ????- | Residue | ????- | ????- | ????- | ????- | ????- |
??C9 | ????- | ????- | Residue | ????- | ????- | ????- | ????- |
??C6 | ????- | ????- | ????- | Residue | ????- | ????- | ????- |
??PAO3 | ????- | ????- | ????- | ????- | Residue | ????- | ????- |
??POE1 | ????- | ????- | ????- | ????- | ????- | Residue | ????- |
??MP | ????- | ????- | ????- | ????- | ????- | ????- | Residue |
Additive | Alkyl diphenylamine | ????0.5 | ????0.5 | ????0.5 | ????0.5 | ????0.5 | ????0.5 | ????0.5 |
Benzotriazole | ????0.03 | ????0.03 | ????0.03 | ????0.03 | ????0.03 | ????0.03 | ????0.03 |
| Trioctyl phosphate | ????1.0 | ????1.0 | ????1.0 | ????1.0 | ????1.0 | ????1.0 | ????1.0 |
Estimate | Rate of evaporation is estimated | ????◎ | ????◎ | ????× | ????× | ????× | ????× | ????×× |
Kinematic viscosity mm
2/s
| ????13.5 | ????12.0 | ????10.4 | ????7.8 | ????8.3 | ????7.5 | ????7.8 |
Kinematic viscosity is estimated | ????× | ????× | ????◎ | ????◎ | ????◎ | ????◎ | ????◎ |
Table 4
| Embodiment |
????1 | ????2 | ????3 | ????4 | ????5 | ????6 | ????7 | ????8 |
????C12 | ????- | ????- | ????- | ????- | ????- | ????- | ????- | ????- |
????C10 | Residue | Residue | Residue | Residue | Residue | Residue | Residue | Residue |
????C9 | ????5 | ????20 | ????- | ????- | ????- | ????- | ????- | ????- |
????C6 | ????- | ????- | ????5 | ????20 | ????- | ????- | ????- | ????- |
????PAO3 | ????- | ????- | ????- | ????- | ????5 | ????20 | ????- | ????- |
????POE1 | ????- | ????- | ????- | ????- | ????- | ????- | ????5 | ????20 |
Alkyl diphenylamine | ????0.5 | ????0.5 | ????0.5 | ????0.5 | ????0.5 | ????0.5 | ????0.5 | ????0.5 |
Benzotriazole | ????0.03 | ????0.03 | ????0.03 | ????0.03 | ????0.03 | ????0.03 | ????0.03 | ????0.03 |
Trioctyl phosphate | ????1.0 | ????1.0 | ????1.0 | ????1.0 | ????1.0 | ????1.0 | ????1.0 | ????1.0 |
Rate of evaporation is estimated | ????◎ | ????◎ | ????○ | ????○ | ????○ | ????○ | ????○ | ????○ |
Kinematic viscosity mm
2/s
| ????11.78 | ????11.65 | ????11.74 | ????11.00 | ????11.78 | ????10.74 | ????11.74 | ????10.97 |
Kinematic viscosity is estimated | ????○ | ????○ | ????○ | ????○ | ????○ | ????○ | ????○ | ????◎ |
Table 5
Composition | Comparative example |
????8 | ????9 | ????10 | ????11 | ????12 |
Cooperate | ????C12 | ????- | ????- | ????- | ????- | |
????C10 | Residue | Residue | Residue | Residue | Residue |
????C9 | ????2 | ????40 | ????- | ????- | ????- |
| ????C6 | ????- | ????- | ????2 | ????40 | ????- |
????PAO3 | ????- | ????- | ????- | ????- | ????2 |
????POE1 | ????- | ????- | ????- | ????- | ????- |
????MP | ????- | ????- | ????- | ????- | ????- |
Additive | Alkyl diphenylamine | ????0.5 | ????0.5 | ????0.5 | ????0.5 | ????0.5 |
Benzotriazole | ????0.03 | ????0.03 | ????0.03 | ????0.03 | ????0.03 |
Trioctyl phosphate | ????1.0 | ????1.0 | ????1.0 | ????1.0 | ????1.0 |
Estimate | Rate of evaporation is estimated | ????○ | ????× | ????○ | ????× | ????○ |
Kinematic viscosity mm
2/s
| ????11.95 | ????11.49 | ????11.91 | ????10.10 | ????11.85 |
Kinematic viscosity is estimated | ????× | ????○ | ????× | ????◎ | ????× |
Table 6
Composition | Comparative example |
????13 | ????14 | ????15 | ????16 | ????17 |
Cooperate | ????C12 | ????- | ????- | ????- | ????- | ????- |
????C10 | Residue | Residue | Residue | Residue | Residue |
????C9 | ????- | ????- | ????- | ????- | ????- |
????C6 | ????- | ????- | ????- | ????- | ????- |
????PAO3 | ????40 | ????- | ????- | ????- | ????- |
????POE1 | ????- | ????2 | ????40 | ????- | ????- |
????MP | ????- | ????- | ????- | ????3 | ????39 |
Additive | Alkyl diphenylamine | ????0.5 | ????0.5 | ????0.5 | ????0.5 | ????0.5 |
Benzotriazole | ????0.03 | ????0.03 | ????0.03 | ????0.03 | ????0.03 |
Trioctyl phosphate | ????1.0 | ????1.0 | ????1.0 | ????1.0 | ????1.0 |
Estimate | Rate of evaporation is estimated | ????× | ????○ | ????× | ????× | ????×× |
Kinematic viscosity mm
2/s
| ????10.35 | ????11.84 | ????10.00 | ????11.89 | ????10.06 |
Kinematic viscosity is estimated | ????◎ | ????× | ????◎ | ????× | ????◎ |
The measuring method of rate of evaporation is as follows.
Container: φ 37 * 50
Lubricants capacity: 10g
Laying temperature: 120 ℃ (thermostatic bath)
Storage period: 300 hours
Mensuration is qualified from the weight decrement of initial weight less than 5 weight %.
Judgement criteria
◎: less than 2.0 weight %
More than zero: 2.0 weight %, less than 5 weight %
*: 5 weight % above (defective)
* *: 10 weight % above (defective)
The mensuration of kinematic viscosity is according to JIS K2283, the kinematic viscosity 11.8mm in the time of 40 ℃
2/ s is above to be defective.
◎: less than 11mm
2/ s
Zero: 11mm
2/ s is above less than 11.8mm
2/ s
*: 11.8mm
2/ s above (defective)
Find out that by table 3 and Fig. 1 dicarboxylic diester oil is because the carbonatoms of di-carboxylic acid for rising rapidly at 9 rate of evaporation when following, is dicarboxylic diester more than 10 so must use carbonatoms.In addition, the kinematic viscosity in the time of 40 ℃ reduces for minimizing with carbonatoms, if carbonatoms for being below 10, then is less than 13mm
2/ s.Therefore, it is that the ester that 10 di-carboxylic acid forms is a principal constituent that the present invention is chosen in rate of evaporation, carbonatoms that kinematic viscosity two aspects are all qualified, by mixing minor component is the low lubricating oil of ester of viscosity ratio principal constituent, adjusts and not only keeps the evaporation characteristic of principal constituent but also can further reduce kinematic viscosity (40 ℃).In addition, as the carbonatoms that is used for principal constituent the pure composition of 10 di-carboxylic acid,, but consider preferred octanol so long as monohydroxy-alcohol does not just have any problem from the aspect of viscosity, stability.
As the low-viscosity oil that minor component is used, in order to reduce the mixing oil viscosity, preferred viscosities likens to and is the low low-viscosity oil of the viscosity of the ester of principal constituent.When using flash-point to be lower than 150 ℃ low-viscosity oil, also encourage evaporation even carry out the mixing of optimum quantity.
Result by table 4~table 6 finds out, though also depend on the kind as the low-viscosity oil of minor component, when ratio surpassed 20 weight %, rate of evaporation rose rapidly.Because the composition of low-viscosity oil is big, estimate that the strong influence of performance, rate of evaporation increase.Therefore, the composition of low-viscosity oil must be below the 20 weight %.When the composition of low-viscosity oil was 3 weight %, the viscosity during with 0 weight % did not have too big difference, but according to carrying out the blended low-viscosity oil, can satisfy two specific characters of viscosity, evaporation sometimes.Though only be 3 weight %, the effect that satisfies two specific characters is big.When especially carbonatoms is 8 DOZ as the low-viscosity oil of minor component, can obtain optimal results.Consider that from the aspect of low-temperature fluidity, intermiscibility, oilness preferred DOZ is as minor component.
Illustrated among Fig. 2 as typical example, in carbonatoms is the diester of 10 di-carboxylic acid, mixed as the rate of evaporation of the lubricant of the DOZ of minor component and the measurement result of kinematic viscosity.
As previously mentioned, the viscosity of clearly visible because lubricant, evaporation characteristic respectively with torque, the weather resistance correlate of the electric motor that the bearing assembly that uses its lubricant is housed, so use the low viscosity and the agent of evaporation characteristic excellent lubrication of system of the present invention in the bearing assembly, can have the low torqueization of electric motor concurrently, long lifetime.
Can be listed below as the bearing assembly that uses lubricating oil of the present invention.
The a of Fig. 3 is the sectional view of an example of expression fluid dynamic pressure bearing.11 is sleeves among the figure, and what mark same sequence number also is identical title at Fig. 4 and Fig. 5.This fluid dynamic pressure bearing is established dynamic pressure grooves the either party at least of axle periphery and sleeve inner peripheral surface, inject lubricating oil or adopt vacuum-impregnated method packing lubrication oil to the gap of its periphery and sleeve inner peripheral surface (play of bearing part), the velocity pressure of the lubricating oil that produces by rotating with the axis is radially rotated back shaft.Fig. 3 b is illustrated in to establish thrust bearing part 8 among the above-mentioned a again, and rotation is supported radially, the sectional view of an example of fluid dynamic pressure bearing of thrust two direction types.Thrust bearing forms by the flange 3 of axle with the sleeve 11 and the base plate of its relative shape processing assembling, the relative part of flange surface part relative and flange surface and base plate with telescopic respectively at least the either party establish dynamic pressure grooves, similarly inject lubricating oil by fluid dynamic pressure bearing shown in axial thrust bearing two sides and a, utilize velocity pressure effect that lubricating oil produces with the rotation of axle can radially, thrust direction two direction back shafts.Moreover, though a of Fig. 3 and b are provided with dynamic pressure grooves, also can be the fluid bearing that does not have dynamic pressure grooves.
Fig. 4 is the sectional view of an example of expression stephanoporate oil-retaining bearing device.The a of Fig. 4 is that bearing surface is circular circular journal bearing, and the b of Fig. 4, the C-1 of Fig. 5 and C-2 are velocity pressure type stephanoporate oil-retaining bearings.The a of Fig. 4 and b be bearing surface only for the radial type, these be with in advance in bearing body the stephanoporate oil-retaining bearing 2 of immersion lubrication oil be pressed into cover parts 5.Be fixed on the electric motor with state, the axle 4 of fixed rotor inserted bearing bore diameter portions use with riveted joint, bonding etc. method fixed bearing assembly.If desired, also can before inserting, axle inject lubricating oil in right amount at the bearing bore diameter face.The inverted rotor side of cover parts seals with gasket in order to prevent oil leakage.Also can use the bottom to make the cover parts of glass type in advance.
In addition, the C-1 of Fig. 5 and C-2 are the aperture surface and sides of velocity pressure type sintered metal bearing, also at the cover tube bottom bearing portions is arranged respectively, the situation that also has radially, axially rotates support belt spindle flange 7 fully non-contactly, the type be in sleeve behind assembling axle, bearing, the gasket in device immersion lubrication oil, and electric motor assemble and use.Since in the space of device thorough impregnation lubricating oil, in device, do not have the residual of air, so in the running at bearing portions formation successive oil film, guarantee high running accuracy, do not worry thermal expansion leakage of oil simultaneously because of air.This type can be brought into play high running accuracy in all use postures, so be preferred for HDD or portable video frequency camera etc., the use posture traverse or the handstand of spindle drive motor, the rotation support of perhaps fixing and so on purposes.Such bearing assembly can directly be fixed on the electric motor, and the front end that rotor is fixed on the flanged pin axle uses.Moreover, shown in C-2, also can be the sleeve divergence type that sleeve is divided into two bodies of cylindrical portions may 9 and thrust support section 10.
As described above, the viscosity of lubricant, evaporation characteristic are owing to have relevant respectively with torque, the weather resistance of the electric motor that the bearing assembly that uses its lubricant is housed as can be seen, so, can have low torqueization, the long lifetime of electric motor concurrently by using the low viscosity and the agent of evaporation characteristic excellent lubrication of system of the present invention in the bearing assembly.Here, confirm example, be set forth in the long duration test result on the spindle drive motor that uses above-mentioned bearing assembly as it.Fig. 9 is the example that loads the bearing assembly of the pressure-type sintered metal bearing shown in the b that uses Fig. 4 on the multi-point scanning electric motor.In addition, Figure 10 is the example of bearing assembly shown in the C-1 of Stowage Plane 5 on the HDD spindle drive motor.Figure 11 shows the result who under the following conditions multi-point scanning electric motor shown in Figure 9 is carried out long duration test.
The long duration test condition
Lubricating oil: comparative example 2, embodiment 1
Speed of rotation: 30000rpm
Ambiance temperature: 60 ℃
Electric motor posture: 40 ° of inclinations
Test period: 500,000 cycles (300,000 cycles of market demands)
Operating condition: on/off (36 seconds 1 cycles)
As shown in figure 11, it is low torque (current value is low) that the lubricant oil composition of embodiment 1 is compared with the situation of the lubricant oil composition that uses comparative example 2, and weather resistance also fully satisfies the requirement in market.The invention effect
Fluid dynamic pressure bearing in stephanoporate oil-retaining bearing, the velocity pressure type stephanoporate oil-retaining bearing, is that the ester that 10 di-carboxylic acid forms is principal constituent by using carbonatoms, and the viscosity when mixing 40 ℃ is lower than 11mm
2The lubricating oil of lubricating oil 3~20 weight % of/s does not damage the weather resistance of the small-sized spindle drive motor usefulness bearing of equipment for information about, can realize low torqueization.